In order to stably operate an electronic circuit, there is a case where it is desired to stabilize power supply voltage to a certain value. Also, the power supply voltage required by each electronic circuit is not necessarily prepared in a device on which the electronic circuit is mounted. In such a case, in order to easily and stably generate the power supply voltage required by the electronic circuit, a regulator circuit is widely used.
The regulator circuit is generally provided with a differential amplifier, an output transistor, and a feedback resistor. The differential amplifier compares output voltage fed back by a feedback resistor with desired reference voltage and controls voltage of a control terminal of the output transistor such that the two voltages approach each other. Therefore, in a case where input voltage or a load fluctuates, the voltage of the control terminal of the output transistor must be changed according to the fluctuation. Patent Documents 1 to 3 disclose techniques of coping with such fluctuation in input voltage and load.